Field of Invention
The invention essentially relates to so-called double-walled or double-cased piping, that is to say pipes formed in the central part of two coaxial tubes, which are an inner tube and an outer tube. Generally speaking, the aim of such a double wall is to leave a ring-shaped space between the two tubes.
Within this scope, the invention more particularly aims to facilitate the manufacture of the ends of such pipes when this ring-shaped space between two tubes must be closed at the ends of the pipes, for whatever reason. This is notably the case when the ring-shaped space between the double-wall acts as a thermally insulating casing for a fluid flowing inside the inner tube.
By way of a preferred area of application, the invention is particularly well adapted to the conditions of manufacture and implementation of such pipes when they are intended to form the successive sections of a continuous pipeline.
2. Description of the Related Art
In this context, reference will notably be made to the case of pipes for the transportation of petroleum products, commonly known as pipelines. In fact, this case is a characteristic example of pipes of great length, more often than not laid in the open sea. To fulfill both technical and economic requirements, these pipes are factory-made, being mass produced as single tubes before being assembled end to end to form the pipeline.
Additionally, these are single tubes of great length (typically 12 or 24 meters) and diameter (around several tens of centimeters), thereby requiring the ends of the tubes to be designed so as to allow a welding machine access to the inner tubes of two consecutive tubes to enable them to be welded end to end without being hindered by their corresponding outer tubes.
Whether said outer tubes are connected by means of a coupling ring or not, it is usual to close off the ring shaped space between the tubes beforehand, at each end of the different tubes, by means of an intermediate coneshaped part that is suitably oriented and-whose circular ends are respectively welded to the inner and outer tubes of the same pipe.
The present invention allows the manufacturing operations to be considerably simplified by avoiding the use of such an intermediate part, and this without losing the functions said part ensures when the pipe is considered as a whole, or compromising the overall performance of the pipe. It also allows manufacturing costs to be reduced and the production rate to, be increased.
To this end, it essentially consists in providing an equivalent coupling between the outer and inner tubes by deforming the outer tube at its end part. Said deformation may be advantageously accomplished, in accordance with the invention, such that an accurate and constant welding play is achieved for the subsequent sealed closing of the ring-shaped space remaining in the central part of the pipe and acting as a thermally insulating casing.
The invention may be embodied in different ways, expressed notably in terms of a manufacturing process for double-walled pipes by deformation of an end part around an end part of an inner tube until they are brought together closing off the ring-shaped space that they form together in the central part of the pipe, or expressed in terms of a device in consideration of a machine incorporating means allowing said process to be implemented. It also relates to means to mass produce double-walled pipes that integrates such a machine.
The subject of the invention is thus a process for manufacturing pipes to be connected in a double-walled pipeline, wherein after having brought the inner tube and the outer tube into relatively coaxial positions arranging a ring-shaped space between them up to a connecting area at the end of the pipe where the outer tube is longitudinally retracted with respect to the inner tube, the wall of an end part of the outer tube is deformed by reducing its diameter until its end joins the inner tube closing off said ring-shaped space, acting concentrically by the gradual application of pressure to its wall by means of a series of bars spaced in a ring around said connecting area and that are tilted over in a radial direction by a crown that is fixed with respect to the outer tube and onto which they are attached in an articulated manner.
Said bars are advantageously tilted over by admitting a gradual fluid build-up in a ring-shaped chamber having flexible walls and of variable volume surrounding the assembly of said bars.
A further subject of the invention is a machine intended to implement the process above, wherein it firstly incorporates a mobile rigid structure to be engaged around a connecting area at the end of the pipe where the end of an outer tube is retracted with respect to an inner tube, said tubes arranging a ring-shaped space between each other, and secondly incorporates active organs incorporating a series of bars spaced in a ring and mounted articulated at a rear end onto a fixed crown of said structure that is common to all of them, as well as means to simultaneously tilt over said different bars in a radial direction so as to incline them and bring their opposing front ends towards the longitudinal axis of their annular arrangement.
Advantageously, said means to tilt over said bars incorporate an inflatable ring-shaped chamber, having flexible walls and of variable volume, surrounding the assembly of said bars, and means to allow a gradual fluid build-up in said chamber.
The rigid structure can incorporate containment means for said chamber when inflated, notably incorporating an external casing, and preferably also an inner side to said casing opposite said crown onto which said bars are articulated.
Advantageously, said rigid structure is fitted with lifting and transportation means to engage it around the connecting area by the free end of the pipe, or to disengage it at the end of the operation, when said bars have been brought into their inactive position away from the outer tube wall.
Still advantageously, said structure incorporates means to guide it when moving along the pipe that cooperate with the outer tube in the central part of the pipe so as to ensure that it is centered longitudinally and radially with respect to the pipe axis, said means preferably incorporating, to the rear of an overhanging beam extending longitudinally away from the pipe, symmetrical rollers intended to keep said beam oriented along an upper generating line of said pipe.
Still advantageously, each of said bars puts pressure of the end part of the outer tube via a foot with which it is fitted and which advantageously has a portion having a longitudinal profile that is inclined with respect to said bar.
Still advantageously, at least concerning the said inclined portion, said foot has a concave transversal profile whose curve radius is preferably of the same magnitude as that of the inner tube.
Still advantageously, said rigid structure incorporates radial guiding rods for the different bars, said rods being attached to a central ring, and provided with a return spring for its corresponding bar to bring said bar back to its inactive position away from the outer tube wall.
Each of said bars is held onto said crown by means of catches abutting on the radial faces of said crown.
Each of said bars is advantageously provided with a thin plate oriented perpendicularly to it and sliding on a finger integral with the rigid structure during the operations designed to tilt over the bars.
Still advantageously, a temporary ring-shaped shim is provided that makes welding play between the end of the outer tube and the wall of the inner tube at the end of the machine""s operations.
Still advantageously, an intermediate layer of a constant though relatively small thickness is provided around said bars, notably to protect the wall of an inflatable ring-shaped chamber.
The invention also relates to means to mass produce pipes to be connected end to end to make a double-walled pipeline, characterized in that it incorporates a machine such as previously described -for the continuous processing of the ends of consecutive pipes.